High strength suture with absorbable core

ABSTRACT

A novel high tensile strength semi-absorbable composite suture with minimized non-absorbable mass. The suture has a core made from a bioabsorbable polymer. The core is covered by a braided sheath. The braided sheath is made from an absorbable yarn and a bioabsorbable yarn. The bioabsorbable yarn is made from a least one filament of a bioabsorbable polymer. The nonabsorbable yarn is made from at least one filament of ultra high molecular weight polyethylene.

TECHNICAL FIELD

The field of art to which this invention relates is surgical sutures, inparticular, surgical sutures having both bioabsorbable and nonabsorbablecomponents.

BACKGROUND OF THE INVENTION

Surgical sutures are well known medical devices in the art. The suturesmay have braided or monofilament constructions, and may be provided insingle-armed or double-armed configurations with a surgical needlemounted to one or both ends of the suture, or may be provided withoutsurgical needles mounted. The sutures are used in a variety ofconventional medical and surgical procedures to approximate tissue,affix or attach implants to tissue, etc. Surgical sutures may be madefrom a variety of known bioabsorbable and nonabsorbable materials. Forexample, sutures are known to be made from aromatic polyesters such aspolyethylene terephthalate, nylons such as nylon 6 and nylon 66,polyolefins such as polypropylene, silk, and other nonabsorbablepolymers. In addition, sutures may be made from polymers and copolymersof p-dioxanone (also known as 1,4-dioxane-2-one), ε-caprolactone,glycolide, L(−)-lactide, D(+)-lactide, meso-lactide, trimethylenecarbonate, and combinations thereof. Of particular utility ispolydioxanone homopolymer.

Surgical sutures are typically available in a range of conventionalsizes for a variety of conventional surgical procedures. The size of thesuture used by the surgeon for any particular procedure is dictated inpart by the type of tissue to be sutured, the relative size of thetissue structure, as well as the forces that will be applied to thesutures by the approximated tissue after the surgical procedure has beencompleted. Similarly, the type of suture selected will be dictated bythe procedure. Nonabsorbable sutures are typically used for applicationssuch as cardiovascular, vascular, orthopedic, gastrointestinal and thelike wherein a nonabsorbable suture is desired or required because apermanent or an extended period of fixation is required during thehealing period, e.g., implantation of a heart valve prostheses.Bioabsorbable sutures are typically used for applications such asplastic surgery, skin fixation and certain soft tissue approximation,and the like. A bioabsorbable suture may be used when extended tissueapproximation or fixation is not required as long as the suturemaintains adequate strength during the healing period, and it isdesirable to replace the suture with autologous tissue such as skin orsoft tissue during the healing process.

In certain applications where significant tensile forces will be appliedon a suture, it is desirable to use materials that will provide hightensile strength with minimal suture size or cross-section. The tensilestrength of a suture is known to be a function of several parametersincluding material, suture size, filament diameter, type of construction(i.e., braided versus monofilament), ratio of sheath to core in abraided construction, type of material in the core, etc. In particularit is known to use ultra high molecular weight polyethylene (hereinafterreferred to as UHMWPE) to construct sutures. Sutures made from ultrahigh molecular polyethylene have the advantage of having high tensilestrength while having a smaller suture size. A disadvantage of suchsutures is that ultra high molecular weight polyethylene is a relativelyslippery material. This inherent slipperiness may affect the knotintegrity of a suture. In a typical surgical procedure, after thesurgeon makes multiple passes of the suture through tissue so that it isproperly approximated and stitched, one or more conventional knots areplaced in the suture by the surgeon to maintain the suture in place andthereby prevent it from loosening. Loosening of a suture may allow theapproximated tissue to split apart, thereby compromising the surgicalprocedure and preventing healing with the potential for causingcatastrophic effects (e.g., anasotomosis graft blow out incardiovascular repairs, implant dislodgement, organ failure, soft tissuedislocation from a bone, etc.).

In order to improve the knot holding characteristics (e.g., knotstrength) of ultra high molecular polyethylene sutures, it is known tocombine the ultra high molecular weight polyethylene yarn component withanother yarn component that has surface friction higher that the ultrahigh molecular weight yarn component. For example it is known to providea ultra high molecular weight polyethylene suture having annonabsorbable core, an ultra high molecular weight polyethylene core oran aromatic polyester core with an outer sheath surrounding the corebraided from a combination of ultra high molecular weight polyethylenefiber yarns and yarns made from fibers of a nonabsorbable material suchas an aromatic polyester. It is also known to have a suture that has anonabsorbable ultra high molecular weight polyethylene core or anaromatic polyester core surrounded by an outer braided sheath braidedfrom a yarn made from ultra high molecular weight polyethylene fibersand a yarn made from fibers of a bioabsorbable polymer.

Although such composite ultra high molecular weight polyethylene suturesprovide increased tensile strength, there are several disadvantagesassociated with their use. One disadvantage is the possibly diminishedknot characteristics that they provide. Typically such sutures produce alarge knot having increased mass, size and/or volume. A knot in anonabsorbable suture remains in the patient's body after the tissue hasbeen approximated and the healing has been completed, and may irritatesoft tissue and cause patient discomfort and pain. It is known that froma medical perspective it is desirable to minimize the mass of an implantin tissue. In addition, it is advantageous for an implant to allow forautologous tissue migration or in-growth to provide for better healing.A bioabsorbable implant such as an absorbable suture permits tissueingrowth as the mass of the implant is resorbed or degraded by thepatient's body to provide for better healing. This healing processallows the patient's tissue to assume the tissue loads as the absorbableportion of the implant or suture resorbs/degrades and loses structuralintegrity and strength. The ultra high molecular weight polyethylenesutures of the prior art have a dense nonabsorbable volume and knotmass, even when combined with a bioabsorbable component, which for themost part remains behind after the tissue healing process has occurred,contributing to problems discussed above.

Accordingly, what is needed in this art are novel composite suturesconstructed from materials providing high tensile strength, andbioabsorbable materials, wherein the composite sutures provide optimaltensile strength with minimal mass of high tensile strength material,and have good knot strength and knot security, and reduced in vivo knotprofile over time, while allowing tissue ingrowth.

SUMMARY OF THE INVENTION

Therefore novel surgical sutures are disclosed. The sutures have a coreof yarn made from filaments of a bioabsorbable polymer. The core issurrounded by a sheath braided from a yarn made from filaments of ultrahigh molecular weight polyethylene and a yarn made from bioabsorbablepolymer fibers.

Yet another aspect of the present invention is a surgical suture. Thesurgical suture has a core and a braided sheath surrounding the core.The core is made from a yarn made from filaments of a bioabsorbablepolymer. The sheath is braided from a yarn made from ultra highmolecular weight polyethylene fibers and a yarn made from bioabsorbablepolymer fibers. The bioabsorbable core and the bioabsorbable fibersinclude one or more active agents including pharmaceuticals,bioceramics, and anti-microbials.

Still yet another aspect of the present invention is a method ofapproximating tissue. A surgical suture is provided. The surgical sutureconsists of a core and a braided outer sheath surrounding the core. Thecore consists of at least one yarn made from filaments of abioabsorbable polymer. The sheath is braided from at least one yarn madefrom ultra high molecular weight polyethylene filaments and at least oneyarn made from bioabsorbable polymer filaments. The suture is stitchedinto a tissue to approximate the tissue and at least one surgical knotis optionally applied to the suture.

Still yet another aspect of the present invention is a method ofimproving absorption profile of the absorbable component of the suture.

Yet another aspect of the present invention is a method of reducing theknot profile of a knot in a surgical suture. A surgical suture isprovided. The surgical suture consists of a core and a braided outersheath surrounding the core. The core consists of at least one yarn madefrom filaments of a bioabsorbable polymer. The sheath is braided from atleast one yarn made from filaments of ultra high molecular weightpolyethylene and at least one yarn made from bioabsorbable polymerfilaments. The suture is stitched into a tissue to approximate thetissue. A surgical knot is made in the suture to secure the suture. Theknot has a knot profile that is reduced as the bioabsorbable componentis absorbed or degraded in vivo over time.

A further aspect of the present invention is a method of providing therelease of active components including pharmaceuticals, andantimicrobials through coatings applied to said sutures.

These and other aspects and advantages of the present invention willbecome more apparent by the following description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-section of a preferred embodiment of asuture of the present invention.

FIG. 1B illustrates an exploded perspective view of the suture of FIG.1A.

FIG. 2A illustrates a profile of a knot tied into a suture of thepresent invention, after the surgeon has emplaced the suture in tissueto approximate the tissue by stitching.

FIG. 2B illustrates the knot of FIG. 2A after the bioabsorbablecomponent has been absorbed, and the knot profile has been reduced.

FIG. 3A illustrates the suture of the present invention mounted to asuture anchor implanted in a bone, wherein the suture secures softtissue to the surface of the bone, prior to the surgical needles beingcut off from the ends of the suture.

FIG. 3B illustrates the suture and suture anchor of FIG. 3A after theneedles have been cut from the suture and a surgical knot has been madein the suture.

FIG. 4 is a graph of In Vitro Knot Tensile BSR % vs. Days presentingdata of Example 4

FIG. 5 is a graph of In Vivo Knot Tensile BSR % vs. Days presenting dataof Example 4.

FIG. 6 is a graft of In Vitro Mass Loss % vs. Days further presentingdata of Example 4

FIG. 7 is a schematic of the testing apparatus for Example 8.

DISCLOSURE OF PREFERRED EMBODIMENT

The ultra high molecular weight polyethylene used to manufacture thesutures of the present invention will typically have a weight averagemolecular weight of about 500,000 g/mole to about 5,000,000 g/mole, moretypically about 1,000,000 g/mole to about 3,000,000 g/mole, andpreferably about 2,000,000 g/mole to about 2,500,000 g/mole. The ultrahigh molecular weight polyethylene typically has a tenacity of about 20cN/dtex to about 40 cN/dtex, more typically about 27.5 cN/dtex to about38.7 cN/dtex.

The ultra high molecular weight polyethylene will preferably be in theform of a conventional yarn having multiple filaments. Such yarns arecommercially available for use in the manufacture of medical devicessuch as surgical sutures. For example, an ultra high molecular weightpolyethylene yarn useful in the sutures of the present invention is 110dtex Dyneema Purity yarn available from DSM, Netherlands.

The bioabsorbable polymers useful to manufacture the sutures of thepresent invention include conventional bioabsorbable and biodegradablepolymers and copolymers. Of particular utility are the syntheticbioabsorbable polymers prepared from lactone monomers selected from thegroup consisting of p-dioxanone (also known as 1,4-dioxane-2-one),ε-caprolactone, glycolide, L(−)-lactide, D(+)-lactide, meso-lactide,trimethylene carbonate, and combinations thereof. These polymers includepolyglycolide, poly(caprolactone-co-glycolide),poly(glycolide-co-lactide), polylactide, polycaprolactone and the likeand equivalents thereof; advantageously the bioabsorbable polymer ispolydioxanone homopolymer. The term “bioabsorbable” as used herein isdefined to mean both bioabsorbable and biodegradable. It is particularlypreferred to use a polydioxanone polymer for the bioabsorbable componentof the sutures of the present invention. The bioabsorbable component ofthe sutures will preferably consist of a yarn containing multiplefilaments made from the bioabsorbable polymer. Methods of manufacturingsuch yarns are known in this art. If desired, although not preferred,the bioabsorbable yarn component may be made of filaments of more thanone bioabsorbable polymer and/or copolymer.

The ultra high molecular weight polyethylene composite sutures of thepresent invention will typically contain about 40 wt. % to about 70 wt.% of bioabsorbable polymer, more typically about 50 wt. % to about 65wt. % of bioabsorbable polymer, and preferably about 52 wt. % to about62 wt. % of bioabsorbable polymer, and more preferably about 62 wt. % ofbioabsorbable polymer. For example, the braided sheath may consist of 45wt. % ultra high molecular weight polyethylene and 55 wt. % ofpolydioxanone, while the core is 100 wt. % polydioxanone, yielding asuture of the present invention consisting of about 38 wt. % ultra highmolecular weight polyethylene and 62 wt. % of polydioxanone.

The composite ultra high molecular weight polyethylene sutures of thepresent invention may have a standard range of conventional suture sizesranging from but not limited to USP standard sizes 9/0 to 5. Theselection of a particular suture size by the surgeon will depend uponseveral factors including type of tissue, size of the wound beingapproximated, tissue load, post operative stresses on the suture,location of the suture, the type of surgical procedure, etc.

The bioabsorbable component of the sutures of the present invention mayinclude various active agents. The active agents that may be added tothe bioabsorbable component of the sutures of the present inventioninclude a variety of pharmaceutical compositions and bone-inducingcompositions, as well as biologics and bio-active materials. The activeagents include, but are not limited to, known anti-inflammatories,anti-infectives, and analgesics or pain killers. The actove agents alsoinclude, but are not limited to, known anti-inflammatories,anti-infectives, and analgesics or pain killers. Examples of specificpharmaceutical compounds include inderal, diclofenac, fenoprofen,ketoprofen, ketorolac, naproxen, bupivicaine, lidocaine, mepivicaine.Examples of antimicrobials include triclosan and chlorhexidinedigluconate. The bone inducing compositions may include known materialssuch as tricalcium phosphate, bioceramics, bioglasses, calcium hydroxyapatite, combinations thereof and the like. If desired, the coatingsused for the sutures of the present invention may contain such activeagents

The amount of such active agents included in the bioabsorbable componentof the sutures of the present invention will be sufficient to provide atherapeutically effective dose. Similarly, the amount of active agentused in a coating will be sufficient to provide a therapeuticallyeffective dose.

The sutures of the present invention will typically be braided fromconventional fiber-containing yarns using conventional braidingequipment. Processes and methods for manufacturing surgical sutures areknown in this art and are disclosed, for example, in U.S. Pat. Nos.5,314,446 and 6,045,071, both of which are incorporated by reference. Inaddition to braiding, sutures typically require one or more additionalconventional process steps after braiding including but not limited tohot stretching, scouring, annealing, coating, tipping, cutting, needle,attachment, packaging and sterilization.

Hot stretch is needed for reducing braid diameter and heat setting theyarns in the braid to prevent so-called “brooming”, when braid edgewould open up or unravel after cutting. The scouring process is requiredfor removal of spin finishes that are applied to the yarns duringextrusion. Annealing is required to remove residual monomer and forincreasing crystallinity. One purpose of a coatings is to provide goodsuture slidability without unduly compromising knot security. Tipping isoptionally needed for a good needle attachment, depending upon thesuture. In addition to spin finish removal, the scouring process alsohelps in removing dust particles and oil droplets that may be depositedduring braiding. At the same time, the scouring agent should not havesignificant adverse effects on suture properties.

It is also known that, in general, coating provides good sutureslidability, e.g., through tissue. Coatings may provide the lubricitynecessary to achieve smooth tiedown and knot slide performance. Whilethis lubricity is required for smooth tiedown, the coating level(s) mustbe precisely controlled in order to maintain knot security.

After a suture is optionally tipped in a conventional manner and cut tolength, needle attachment takes place. Then, the needle/suturecombinations are packaged, and finally sterilized, for example with anEthylene Oxide process, or other conventional sterilization processesdepending on the type of material and packaging, e.g., gamma radiation,autoclaving, plasma, etc.

Referring to FIG. 1, a cross-section of a preferred embodiment of asuture of the present invention is seen. The suture 10 is seen to havean outer sheath 20 and an inner core 40. The sheath 20 is seen to be abraided structure of two yarns in intertwining contact. Yarn 30 iscomposed of filaments of ultra high molecular weight polyethylene. Yarn35 is composed of filaments of a bioabsorbable polymer such aspolydioxanone. The core 60 is seen to be have yarns 70 composed ofbioabsorbable polymer fibers. The yarns 70 are preferably made of thesame bioabsorbable polymer as yarn 35, but alternate embodiments may bemade from a different bioabsorbable polymer.

When used in a surgical procedure, the sutures of the present inventionare typically knotted, ultimately, by the surgeon after stitches havebeen made in tissue to emplace the suture, in order to secure thesuture. The surgical knots that are utilized for this purpose are wellknown to surgeons and medical practitioners and include the followingtypes of knots: surgeon's throw, Revo knot, SNC knot, Tennessee Slider,Modified Roeder, square knot, half-hitch and reverse half-hitch, Duncanloop, etc. As seen in FIG. 2A, a suture 10 of the present invention isseen to have been emplaced in tissue 100 to secure and approximate theedges 115 of a wound 110. A half-hitch and reverse half-hitch knot 130has been tied in the suture 10 to secure stitches 125 in place. The knot130 is seen to have a knot profile characteristic 140. The term knotprofile characteristic is defined to mean the overall mass and volume ofa suture knot including a spatial shape or configuration. The term knotprofile dimension is defined to mean an overall thickness of the knot,for example, when the knot is tied, the ears of the knot will usually belying parallel to the plane of the approximated tissue. The knot 130seen in FIG. 2A has the knot profile characteristic 140 immediatelyafter implantation. The suture 10 of FIG. 2A is illustrated in FIG. 2B,in vivo, after a sufficiently long period of time has passed toeffectively provide for absorption of the bioabsorbable components. Theknot 130 is seen to have a reduced knot profile characteristic 140attributable to the loss of mass and volume of the absorbable component.Surprisingly and unexpectedly, the strength of the knot 130 is notsignificantly reduced, even though the absorbable component of suture 10has been absorbed away from the suture 10. In addition, tissue in-growthis seen to have occurred.

The sutures of the present invention are preferably used in conjunctionwith suture anchors to repair soft tissue injuries. Suture anchors andprocedures using suture anchors are disclosed in the following UnitedStates patents which are incorporated by reference: U.S. Pat. Nos.4,632,100, 4,999,074, 5,814,051, 5,709,708, 5,782,864, 6,270,518,5,540,718, 6,264,674, 6,270,518, 6,306,158, 5,961,538, 5,782,863,5,683,418, 5,554,171, 5,078,730, 4,632,100, 5,217,486, 5,011,473,4,898,156, 4,899,743, 4,946,468, 4,968,315, 5,002,550, 5,046,513,5,192,303, 5,207,679, 5,358,511. As seen in FIGS. 3A and 3B, a suture200 of the present invention is mounted to a conventional bioabsorbablesuture anchor 250. Anchor 250 is seen to have anchor body 255. Thesuture 200 is mounted through suture mounting passage 260 in anchor body255. The anchor 250 is seen to be mounted in a bore hole 275 drilledinto a bone 270. The anchor 250 is mounted in the cancellous portion 280of the bone 270 below the cortex 285 and engages cancellous portion 280.Soft tissue 290 is seen to be approximated to bone surface 287 by suture200. Suture 200 is seen to have conventional surgical needles 340mounted to each end 210. The tissue is secured by placing a half-hitchand reverse half-hitch knot 310 in suture 10. The knot 310 is seen tohave knot profile characteristic 315. Surgical needles 340 are cut fromsuture 200 prior to the completion of the procedure.

It is also known to those skilled in the art that polydioxanoneabsorbable yarns with a relatively small filament diameter (about 3denier per filament or smaller) will lose strength faster than yarns ofthe same total denier that have filaments with substantially largerdenier per filament (e.g. 12 denier per filament). In many surgicalindications, substantial strength needs to be maintained during thecritical wound healing process. There is thus a need to use largerdiameter polydioxanone filaments—higher denier per filament yarns. Onthe other hand, it is a well-known principle that column strength andbending strength of cylinders are both very dependent on diameter. It isthus surprising and unexpected that the bi-component suture that is madewith larger diameter 12 denier per filament (dpf) yarn does not becomestiffer and still retains desirable handling characteristics similar tothe suture made with the much smaller filament diameter yarns (3 dpf).

The following examples are illustrative of the principles and practiceof the present invention, although not limited thereto.

EXAMPLE 1

A suture of the present invention was manufactured in the followingmanner. The suture was made using a conventional maple (hollow) braider.The composite suture had a sheath of ultra high molecular weightpolyethylene yarn and polydioxanone yarn. The sheath contained 45 wt. %ultra high molecular weight polyethylene and 55 wt. % polydioxanone. Thecore of the suture consisted of 100 wt. % polydioxanone yarn. Overall,the suture consisted of 38 wt. % ultra high molecular weightpolyethylene and 62 wt. % polydioxanone. The nonabsorbable component ofthe suture construction consisted of eight 100-denier Dyneema Purityultra high molecular weight polyethylene multifilament yarns(manufactured by DSM) that were loaded on the braider in thecounterclockwise direction, and the polydioxanone component was aconventional multifilament polydioxanone yarn, such as that used tomanufacture polydioxanone sutures by Ethicon, Inc., Somerville, N.J. Thepolydioxanone component consisted of eight polydioxanone 60×2 denierdyed multifilament yarns that were loaded on the braider in theclockwise direction. The braid had a core construction that consisted ofdyed polydioxanone 60×2/3 multifilament yarns. Pick count is selected ataround 47-48 ppi. The absorbable core was selected to minimize suturemass in the body after absorption and provide better suture cuttingability. The braid construction is described in the Table 1. TABLE 1Counter Braider Clockwise Clockwise Pick Core Material CarriersDirection Direction Count Construction Dyneema 16 Polydioxanone Dyneema46 Poly- yarn Poly- yarn yarn dioxanone dioxanone 60 × 2/8 100 × 1/8yarn yarn 60 × 2/3

The off-braider material required additional conventional processing inorder to become a suitable suture material. The process flow can bedescribed as follows: hot stretching, annealing, scouring, coating,tipping, and cutting.

The suture was hot stretched at 90° C., which is 5 degrees above theannealing temperature. Such arrangement is needed in order to maintainthe heat set memory acquired by braid during the hot stretch. Due to avery low elongation of Dyneema yarn (about 4%), the percentage stretchwas set at 8%. Such relatively low percentage of stretch does not damagethe braid, and at the same time provides a sufficient force forconsolidating the braid structure.

The material was wound onto the racks, and scoured for about 80 min inacetone. Spin finish residuals were reduced to acceptable levels.

The material was coated with a conventional absorbable coating with aconcentration level of 4.5% (wt./wt.) of a 90/10 copolymer ofcaprolactone/glycolide dissolved in ethyl acetate using a drip process.The suture's unique absorbable/non-absorbable construction has led tothe evaluation of both absorbable and non-absorbable coatings.

In certain surgical circumstances, it may be preferred that the coatingabsorbs prior to the absorption of the polydioxanone component of thesuture.

Since polydioxanone (hereinafter referred to as PDS) material issusceptible to UV light and exposure to ambient air in general, theexposure time limits have to be maintained during suture processing.

EXAMPLE 2

The tensile strength of the suture of Example 1 was tested in accordancewith the United States Pharmocopoeia using the method for a constantrate of extension. In addition, the tensile strengths of the followingcommercially available sutures were also determined: an aromaticpolyester (hereinafter referred to as PET) suture such as onemanufactured by Ethicon, Inc., Somerville, N.J., and an ultra highmolecular weight polyethylene/PET suture such as FIBERWIRE manufacturedby Arthrex, Inc., Naples, Fla. The results of the testing are presentedin Table 2.

This example compared straight and knot tensile strength of suture ofthe present invention to the FiberWire suture and the PET suture. Thecomparison shows that the use of polydioxanone in the core of the sutureof the present invention had no adverse effect upon the physicalproperties of the suture. In order to compare strength of the suturesthat have slightly different diameters, straight and knot strength wasnormalized to the cross-sectional area of the suture and expressed inKpsi. TABLE 2 Straight Straight Braid Diameter Tensile Tensile Knot KnotI.D. (mils) (lbs) (Kpsi) Elongation % (lbs) (Kpsi) 1 Present 22.87 63.81155.63 13 29.50 71.95 Invention 2 UHMWPE/PET 21.89 51.61 137.19 8 26.7471.08 3 PET 21.29 31.34 87.06 22 15.10 41.94

The test results showed the suture of the present invention hadequivalent or superior tensile strength, and knot break tensile strengththan the ultra high molecular weight polyethylene/an aromatic polyesternonabsorbable suture and the an aromatic polyester suture.

EXAMPLE 3 In Vitro Knot Tensile Breaking Strength Retention (BSR) & MassLoss Over Time

Samples of the suture of Example 1 for In Vitro Knot Security weredegraded in a buffer of pH 7.27 and a water bath with temperature 57° C.Knots were secured with 5 throws and placed in the buffer container.Five knot-secured sutures from each lot were tested for each timeperiod. Sutures were tested before and after degradation using theInstron Tensile Tester employing a Hermann's loop fixture, 2″/min XHspeed to obtain breaking strength. Note: Because this test was a loop,the knot strength was approximately twice that for the typical USP knottensile test. The mass remaining was obtained by drying and weighing thesutures after different times in the buffer solution.

In addition to the suture of Example 1 consisting of about 40 wt. % highmolecular weight polyethylene and about 60% polydioxanone, anothersuture was tested consisting of 100 wt % polydioxanone. Table 3 providesthe in vitro knot strength results versus days in the buffer. The 60/40polydioxanone/ultra high molecular weight polyethylene suture reachedapproximately 30 lb strength after 18 days and was relatively constantthereafter. By design the ultra high molecular weight polyethylenestrength after loss of the polydioxanone was intended to beapproximately 30 lb to match the strength of nonabsorbable an aromaticpolyester sutures. Thus, the strength retention of the polydioxanonecomponent of the polydioxanone/ultra high molecular weight polyethylenesuture was estimated by subtracting 30 lb from the strength for thesuture. This data was also used to present the data as a percentremaining in Table 3 and graphically in FIG. 4. TABLE 3 In Vitro KnotTensile Breaking Strength Retention (BSR) In Vitro Knot Tensile, lb InVitro Knot Tensile, % Days 60/40 PDS/PE 100% PDS PDS Component* 60/40PDS/PE 100% PDS PDS Component 0 53.8 32.5 23.8 100 100 100 4 54.4 2624.4 101 80 103 7 49.5 20.2 19.5 92 62 82 11 47.3 8.7 17.3 88 27 73 1440.2 4.1 10.2 75 13 43 18 30.6 1.6 0.6 57 5 3 21 31.2 0.6 1.2 58 2 5*Based on subtracting 30 lb for the UHMW PE component per the design.

It was not anticipated that the polydioxanone in thepolydioxanone/polyethylene suture would maintain higher strength overtime than for a 100% polydioxanone braided suture.

In Table 4 and FIG. 5, the weight remaining for the knotted suture ispresented. The calculation for percent weight remaining for thepolydioxanone component of the bicomponent suture was based on the factthat the suture design was 40 wt. % high molecular weight polyethyleneand 60 wt. % polydioxanone. So the wt. % remaining for the polydioxanonecomponent is obtained by subtracting 40 percent from the bi-componentsuture and dividing by 0.60.

Note that the weight loss for the polydioxanone component of thebicomponent suture was not atypical of that obtained for the 100%polydioxanone suture. Thus it becomes even more surprising that the knotstrength retention in the polydioxanone component of the bicomponentsuture remains higher than expected while the mass loss is as expected.This feature is highly desired to maintain good strength yet decreasemass. TABLE 4 In Vitro Mass Loss Days 100% PDS 60/40 PDS/PE PDSComponent* 0 100 100 100 4 100 100 100 7 101 102 103 11 99 102 103 14 9598 97 18 84 89 82 21 79 81 68 30 26 48 13*Based on subtracting the 40% by weight for the UHMWPE component anddivide by 60% which was the starting content of the PDS.

EXAMPLE 4 In Vivo Knot Tensile Breaking Strength Retention (BSR)

In vivo breaking strength retention was conducted for the suture ofExample 1 in the following manner.

The method used for in vivo knot tensile was the same as for the invitro testing except four knot-secured sutures were implanted from eachlot, for each time period, using two rats. One of each knot securedsutures were implanted right and left posterior dorsal subcutis.Explanted sutures were examined visually and microscopically: it wasnoted that there was slight growth of tissue around the suture as aresult of time, not as a result of suture composition. Sutures weretested on the Instron Tensile Tester using Herrmann's loop fixture,2″/min XH speed to obtain breaking strength.

Analysis of this data is displayed in Table 5 and FIG. 6 and gave verysimilar results to the in vitro data. The difference between the knotstrength retention for the PDS component of the composite braid from the100% PDS is even more pronounced for in vivo implantation than for thein vitro testing. Again this is a highly desirable feature and is notanticipated. TABLE 5 In Vivo Knot Tensile Knot Tensile, lb Knot Tensile,% Days 60/40 PDS/PE 100% PDS PDS Component 60/40 PDS/PE 100% PDS PDSComponent 0 52.9 31.7 22.9 100 100 100 21 54.2 12.0 24.2 102 38 106 3553.7 6.0 23.7 102 19 103 42 54.3 4.0 24.3 103 13 106 49 50.7 4.8 20.7 9615 90 63 44.9 2.9 14.9 85 9 65

EXAMPLE 5 Knot Profile Reduction (Boil Out Test)

An accelerated absorption test (boil-out) in 0.05N Sodium Hydroxidesolution was conducted using coated suture of Example 1 to verifywhether suture knot profile was being reduced after the polydioxanonecomponent was absorbed.

Five samples were prepared by tying loops in the suture, each having aknot consisting of five surgeon's throws. Each sample was labeledaccordingly. The thickness of each knot was measured and recorded usinga Mitutoyo digital gauge. The measurement was performed with the sutureloop lying on the anvil and with the knot being placed between thecenter of the anvil and the micrometer foot. A 500 ml Pyrex bottle with0.05N Sodium Hydroxide solution was prepared. The knots were placed intothe bottle, with the bottle sealed using a tight lid. The bottle wasthen placed into a water bath at 90° C. for about twenty-four hours.

After twenty-four hours “boil-out”, the samples were removed from thebottle and dried for one hour. The thickness of each knot was measuredagain. The results are exhibited in the Table 6 below. TABLE 6 Knot KnotThickness Thickness Before After Absorption, Absorption, mils mils 180.45 31.40 2 68.50 37.15 3 66.45 36.65 4 76.25 38.00 5 75.95 43.45 Avg73.52 37.33 Std.Dev. 5.84 4.29

This experiment demonstrates that the knot profile was reduced by about50% after the bioabsorbable polydioxanone component is absorbed. Thesuture flattens, making the knot less palpable and thus, reducing tissueirritation.

In another experiment, an in vitro absorption test was conducted usingthe coated suture of Example 1.

Samples were prepared by tying loops in the suture, each having a knotconsisting of six half hitch knots, alternating throw, alternatingposts. Each sample was labeled accordingly. The samples were placed inphosphate buffered solution at 57° C. for a period of 26 weeks. Thesamples were weighed and the volume of the samples was calculated. Theseresults were compared to Day 0 samples. The results are shown in Table 7below. TABLE 7 Day 0 26 week % Reduction Mass 0.033 g 0.013 g 60% Volume 39.4 mm³  24.8 mm³ 40%

EXAMPLE 6

In this example, an antimicrobial, Triclosan, is blended with a powderedform of a biodegradable polymer such as polydioxanone. The blending iscarried out in a Brabender, Baker Perkins Blender, or a V-blender, andis generally although not necessarily done at an elevated temperature.Solvents may be added if desired to help improve the blending; thedispersing solvent is then generally removed prior to extrusion. Theresulting composition is extruded using a single or twin extruder, orpelletized. Once blended, the material was re-extruded using aconventional single or twin screw extruder with a die that is capable offorming a monofilament or multifilament fiber. This fiber is eithercollected directly from the spinneret with no other modification, or itcan be optionally post processed by annealing and drawing. Resinthroughput, take-up speed and the extent of drawing dictate the diameterand degree of orientation of the fiber. The fiber is spun into a yarn.

EXAMPLE 7

The absorbable multifilament yarn of Example 6 is used to make acomposite suture of the present invention by following the process ofExample 1 and substituting the yarn of Example 6 for the bioabsorbableyarn of Example 1.

EXAMPLE 8 Bending Stiffness Test

Five suture strands 1.5 inch in length were prepared from each lot fortesting. A special fixture (described below) was used with the InstronTensile Tester (Model 4201) to measure the resistance of the forcerequired to pull the suture through the opening in the fixture. A loadcell of 500 g was used for this test. The crosshead speed was one inchper minute. The information from the test was gathered electronically.

The upper portion of this fixture is illustrated in FIG. 7. The fixture502 consists of the metal rod 506 with a passage 508 at the end of therod for threading the suture 510 through. The upper end of the rod wasconnected to load cell 505. The lower portion of the fixture consists ofa bracket 512 attached to the machine base 514. That bracket has anopening 516 is 10 mm, which was slightly larger than the diameter of rod506. The center of this opening 516 was lined up with the center of themetal rod.

Five samples of 1.5 inch each of the suture of Example 1 were prepared.Each sample was inserted through passage 508 in the metal rod untillength of suture on each side of opening was about the same. Then, thecrosshead was getting started and the suture was pulled through openingin the bracket. When the suture sample was pulled through the opening inthe bracket, the resistance in grams is being recorded. Five sampleswere measured and the results were averaged to provide the reportedvalues.

The results as presented in Table 8 demonstrate that thepolyethylene/polydioxanone suture of the present invention had betterbending stiffness than FiberWire polyethylene/an aromatic polyestersuture, and had similar properties to an aromatic polyester suture.TABLE 8 Bending Stiffness Test Results Present UHMWPE/PET UHMWPE/PET PETInvention Stripped Blue Average 0.816 0.986 1.849 3.195 Stiffness, gramsSt Dev 0.148 0.239 0.601 0.295

EXAMPLE 9

A patient is prepared for rotator cuff surgery in a conventional manner.The patient is anesthetized using conventional anesthesia. The pathologyis identified and diagnosed arthroscopically using a conventional trocarand a conventional arthroscope. The surgeon views the site of the injuryusing a conventional arthroscope inserted through a cannula that isemplaced in the shoulder adjacent to the injury site. The surgeonreleases any adhesions, debrides the lateral margin of the rotator cuff,immobilizes the tendon and prepares the bone bed. The surgeon locates anoptimal suture anchor placement site on the ‘downside’ of the greatertuberosity of the patient's humeral head and drills a bone bore hole foranchor emplacement in the following manner. A drill guide is insertedthrough the trocar. A drill bit is placed through the drill guide andthe bore hole is drilled for the suture anchor. A conventional sutureanchor such as the suture anchor illustrated in FIG. 3 having a sutureof the present invention mounted thereto is inserted and emplaced in thebore hole engaging the cancellous bone below the bone cortex. Surgicalneedles attached to the ends of the suture are used to penetrate thesoft tissue (i.e., tendon) such that the soft tissue is approximated tothe surface of the bone. The suture is then knotted in a conventionalmanner using a conventional surgical knot. The needles are then cut fromthe suture and the procedure is then complete and the patient's externalfascia and skin are approximated in a conventional manner by suturing orusing surgical tape or surgical glues.

The sutures of the present invention have many advantages. Theadvantages include maximized suture mass reduction over time, reducedknot profile over time, improved BSR profile, and high tensile strength,and improved handling characteristics.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

1. A surgical suture, comprising: an inner core comprising at least oneyarn comprised of at least one fiber, said fiber comprising abioabsorbable polymer; and, an outer braided sheath comprising a secondyarn comprised of at least one nonabsorbable fiber and a third yarncomprising at least one bioabsorbable fiber, wherein the first andsecond yarns are in intertwining contact.
 2. The surgical suture ofclaim 1, wherein the bioabsorbable first and bioabsorbable second yarnscomprise a polymer prepared from lactone monomers selected from thegroup consisting of p-dioxanone, ε-caprolactone, glycolide,L(−)-lactide, D(+)-lactide, meso-lactide, trimethylene carbonate, andcombinations thereof.
 3. The surgical suture of claim 1, wherein thenonabsorbable fiber comprises ultra high molecular weight polyethylene.4. The suture of claim 1, wherein the suture comprises about 55 wt. % toabout 70 wt. % of bioabsorbable polymer.
 5. The suture of claim 2,wherein the bioabsorbable yarns comprise polydioxanone.
 6. The suture ofclaim 1, wherein the bioabsorbable first and second yarns comprise apharmaceutical composition.
 7. The suture of claim 6 wherein the firstand second yarns comprise a pharmaceutical composition selected from thegroup consisting of analgesics, antibiotics, anti-inflammatories, andpain killers.
 8. The suture of claim 1 wherein the polyethylene yarncomprises an ultra high molecular weight polyethylene having a weightaverage molecular weight of about 500,000 to about 5,000,000 g/mole. 9.The suture of claim 1, additionally comprising a coating.
 10. The sutureof claim 1 additionally comprising a surgical needle mounted to one end.11. A method of approximating tissue, comprising: providing a suture,said suture comprising: an inner core comprising at least one yarncomprised of at least one fiber, said fiber comprising a bioabsorbablepolymer; and, an outer braided sheath comprising a second yarn comprisedof at least one nonabsorbable fiber and a third yarn comprising at leastone bioabsorbable fiber, wherein the first and second yarns are inintertwining contact stitching said suture through tissue; and, tying aknot in the suture.
 12. The method of claim 11, wherein thebioabsorbable first and bioabsorbable second yarns comprise a polymerprepared from lactone monomers selected from the group consisting ofp-dioxanone, ε-caprolactone, glycolide, L(−)-lactide, D(+)-lactide,meso-lactide, trimethylene carbonate, and combinations thereof.
 13. Themethod of claim 11, wherein the nonabsorbable fiber comprises ultra highmolecular weight polyethylene.
 14. The method of claim 11, wherein thesuture comprises about 55 wt. % to about 70 wt. % of bioabsorbablepolymer.
 15. The method of claim 12, wherein the yarns comprisespolydioxanone.
 16. The method of claim 11, wherein the bioabsorbablefirst and second yarns comprise a pharmaceutical composition.
 17. Themethod of claim 16 wherein the first and second yarns comprise apharmaceutical composition selected from the group consisting ofanalgesics, antibiotics, anti-inflammatories, and pain killers.
 18. Themethod of claim 11 wherein the polyethylene yarn comprises an ultra highmolecular weight polyethylene having a molecular weight of about 500,000to about 5,000,000 g/mole.
 19. The method of claim 11, additionallycomprising a coating on the suture.
 20. The method of claim 1additionally comprising a surgical needle mounted to one end of thesuture.
 21. The suture of claim 1, wherein the first and second yarnsadditionally comprise a bioceramic material.
 22. The suture of claim 1,wherein the first and second yarns comprise a material selected from thegroup consisting of tricalcium phosphate and hydroxyapatite.
 23. Themethod of claim 11, wherein the first and second yarns additionallycomprise a bioceramic material.
 24. The method of claim 11, wherein thefirst and second yarns comprise a material selected from the groupconsisting of tricalcium phosphate and hydroxyapatite.
 25. A method ofreducing the knot profile of a knot in a surgical suture, comprising:providing a suture, said suture comprising: an inner core comprising atleast one yarn comprised of at least one fiber, said fiber comprising abioabsorbable polymer; and, an outer braided sheath comprising a secondyarn comprised of at least one nonabsorbable fiber and a third yarncomprising at least one bioabsorbable fiber, wherein the first andsecond yarns are in intertwining contact stitching said suture throughtissue; tying a knot in the suture, said knot having a knot profile;and, maintaining the knot in the suture in vivo for a sufficient periodof time to effectively reduce the knot profile.
 26. The suture of claim5 wherein the yarn comprises a filament having a denier greater than 3denier per filament.
 27. The suture of claim 5 wherein the yarncomprises a filament having a denier greater than 12 denier per filamentwithout substantial adverse effect to suture handling and stiffness whencompared to the commercially available sutures prepared from ultra highmolecular weight polyethylene/PET.
 28. The suture of claim 5 wherein theyarn comprises a filament having a denier greater than 12 denier perfilament without substantial adverse effect to suture handling andstiffness when compared to the sutures prepared from polyethyleneterephthalate with a denier per filament less than 3.